Electron transfer between a quinone or quinoid molecule occurs in the energy conversion systems of many organisms. Studies are being carried out to investigate intra- and intermolecular electron transfer reactions involving quinone complexes. Rates of intramolecular metal-quinone electron transfer have been estimated to be 10 to the ninth power sec to the minus one power. Catecholate ligands destabelize terminal oxo ligands bonded to Mo (VI). Oxygen atom transfer reactions to/from a Mo (VI) center in the manner of certain molybdoenzymes have become a focus of interest. Studies are also being carried out on the reductive activation of small substrate molecules (02,NO) at an oxidized metal center bonded to reduced quinone ligands. Complexes of V(V) and Mn(III) are being used in this investigation, with catecholate oxidation to semiquinone facilitate 02 reduction.